The field of the invention is in the instrumentation art and more particularly in the indicator monitoring art.
The need of reliable instrumentation is well known. Various means have been devised over the years to verify if a gage, a pointer, or a meter is indicating a true value. One of the simplest means is the redundancy of multiple systems and indicators. This technique is very space consuming, costly, and complicated. The common state of the art method is to present only a single indication but to compare or monitor this indication electrically with another value indicative of the same parameter but derived through a different system. When a departure from equivalency of the two systems is detected by the monitor an indication such as an audible alarm, a light, or an indicator flag is raised to indicate to the observer that a defect exists in the system with a possible erroneous indication being presented. These redundancy systems as previously stated, are expensive, bulky, complicated and through the additional coupling to the parameter being sensed, increases the possibility of detrimental effects occurring in the operation being sensed. Some prior art instrument flight indicator monitors will give an indication of error for different instrument indications when the monitoring system is functioning, but will not sense a failure in the monitoring system.
The best known prior art is that of U.S. Pat. Nos. 3,439,321 to patentee Sebern; 3,685,034 to patentee Hedrick; 2,603,696 to patentee McEwan; and 3,778,760 to patentee Jayne.